Offshore energy storage device

ABSTRACT

An aggregate to store energy as kinetic energy, includes a float body and conversion element. The float body is at least partially placed in a liquid and arranged to rotate in direct contact with the liquid and the float body is used by the aggregate to store energy in form of movement together with the surrounding liquid. Energy is supplied or extracted from the float body and surrounding liquid via conversion element or via a part that absorbs energy of movements in a fluid. The aggregate could further include the conversion element or the part that absorbs energy of movements. The energy is supplied or extracted from the float body and the surrounding liquid or from a combination of these.

TECHNICAL FIELD

The present invention relates to an offshore energy storage device,storing energy as rotational kinetic energy, comprising an elongate,upright central part, which is rotatable around its longitudinal axis,floating means arranged to keep it upright and floating, a fly wheelarranged concentrically around the central part and anchorage meansbelow the fly wheel for anchoring to the sea bed.

BACKGROUND ART

Motions in air and water are a concentrated form of renewable energyresources that hold great opportunities to provide energy in anenvironmentally friendly way. And humans have used these resources forthousands of years. The energy has partly been absorbed and converted byvertical axis power plants, meaning that the part of the power plantthat absorbs the energy is located on an axis that is verticallydirected, and partly by horizontal axis power plants, meaning that thepart of the power plant that absorbs the energy is located on an axisthat is horizontally directed.

However the usage of power plants to absorb motions in air and water hasbeen limited, especially in oceans with depths over 50 meters. Theseareas hold large quantities of energy that is bound in motions but ithas been very expensive to install power plants on these locations andlarge foundations or attachments to the ground have often been used.

A previous power plant that has solved some of these problems is thepatent application EP1106825A, which comprises an aggregate to absorbmotions in the air where a float body is used to install a wind-powerstation on top of it. U.S. Pat. No. 4,775,340 is also a similar exampleof this; here is the floating frame, that the wind-power station isplaced on, round in the horizontal plane.

But the power stations must also be stable since water and air flow canvary quickly. A good solution to this is described in the patentUS2006269396, where a floating wind-power station floats in a verticalposition so that the centre of mass of the power plant is located underthe centre of the buoyancy. That power plant is trying to get a goodstability through a vertical extent while the U.S. Pat. No. 7,397,144B1instead discloses a horizontal extent, which makes it possible to builda very large and heavy rotor with no bearings. This patent, U.S. Pat.No. 7,397,144B1, describes an aggregate to absorb the motions in the airwhere both float body and rotor together rotate as a floating body onthe water.

The U.S. Pat. No. 7,397,144B1 discloses a vertical axis power plant, butunlike the previously mentioned power plants, it uses a rotating surfacebased float body with a horizontal extent. To rotate the body which hasa large extent horizontally means, however, that friction will increasebecause of the higher speed on the outer parts of the float body. Thehorizontal extent also means that strong forces are acting thereon instormy weather and large waves, since the surface towards the waves arelarge, which in turn makes high demands on anchorage and the ability towithstand very large forces. The remaining problems for the devicedisclosed in U.S. Pat. No. 7,397,144B1 and the previous technologies arestill stability and, as a result of this, also anchoring.

Another major problem for renewable energy resources is also that theyusually do not have a continuous out-effect, for example, it varies dueto wind variations. Being able to store energy in a suitable and costefficient way is still a major problem. The power plants mentioned abovemay therefore be positioned at locations with a relatively stableclimate, and in combination with other energy systems, for examplehydropower, so that a consumer of energy can get a reliable, continuousdelivery of energy, even if there is, for example, no wind.

Even if we make use of for example the storage capability of hydro powerthere is a limit to how many power plants mentioned above that can beincorporated in an energy system. This is one of the reasons forstarting to explore different solutions, such as the present invention.

SUMMARY OF THE INVENTION

The present invention relates to an aggregate to store energy as kineticenergy. The aggregate comprises a float body intended to be placed, atleast partially, rotating in a fluid. The present invention relates tothis aggregate as well as the use of such aggregates.

The present invention uses, in fact one of the earlier overlookedphysical effect in power plants, the conservation of angular momentum.By rotating a relative heavy object around an axis, the object willresist to changes in its orientation. This is used by the presentinvention to create stability but also to be able to store energy likein a flywheel.

Another, maybe even more important, solution in the present invention isthe use of inertia and the weight of the surrounding water thatstabilizes the aggregate when it rotates with a vertical extent down inthe depth of the water. This stable and rotating platform can besupplied with energy through a conversion means, for example a generatorand motor, or by wind or water blades that absorbs the energy from themoving air or water. In this way the present invention can work as areservoir for example the above mentioned aggregate in U.S. Pat. No.7,397,144B1 or other power plants.

Another invention that converts wave motions of the ocean is describedin international patent application WO2008038055 and uses two floatingcylinders which are driven by the wave motions. The present invention,however, does not receive its rotation from wave motions and does notconsist of two floating bodies and these are not situated at the surfaceof the ocean, which makes it impossible for the surrounding water tostabilize as in the present invention.

The present invention can incorporate a section that absorbs wind as avertical wind-power plant. In this way the section that absorbs theenergy when it blows can also store this energy as kinetic rotationenergy in all the rotating parts of the aggregate. When the wind hasstopped blowing, the aggregate or maybe just parts of the aggregatecould continue to spin even though the parts that absorb the energy havestalled. This means that the conversion means of the invention, forexample a generator can generate energy even when it no longer blows.

By these aspects the present invention differs significantly frompreviously known technologies and by distinguishing in this way, powerplants can be developed for e.g. storing energy, creating a smallersurface against the waves and thereby resisting storms better, handlingvariations in wind or water flow by having better stability and also beused by existing energy producing power plants to store energy in theform of rotation and to provide a better stability in energy systems. Inthe last case, for example, a generator could be used reversed as anelectrical motor where the energy will be converted from electricity tokinetic energy, and later be converted back to electric energy whenneeded.

Storing energy in rotation through flywheels has been known for a longtime, but the units that have been built have often used complicatedconstructions and technology where the rotor is suspended by bearings ormagnetic fields and where the rotor often rotates in a vacuum todecrease the friction. Instead of building complex units with a rapidlyrotating rotor, large and simple units will built, using naturalcomponents such as the surrounding water as a bearing.

A first object of the present invention is to provide an aggregate thatcan store energy as kinetic energy. In this way, energy systemsconnected to the aggregate can be more stable and the aggregate can workas energy reservoir, even for other power plants that transports itsenergy to the aggregate for storage. The energy production of the powerplants will benefit significantly through storage of energy, since theenergy that is produced when demand is low and there are high winds alsocan be used if stored.

A second object of the present invention is to provide an aggregate thatextracts energy from the movement of air and water in a cost efficientway. This is partly done by building a very large power plant and partlyby using relatively cheap material in the construction, since weight isnot as limiting a factor as in previous techniques.

A third object of the present invention is to provide an aggregate withas few moving parts as possible, to minimize the risks of damage undersevere weather conditions, for example.

A fourth object of the present invention is to provide a stableaggregate which efficiently can handle the variations in air and waterflow.

A fifth object of the present invention is to provide an aggregate whichis easy to install and which also becomes mobile after the installation.

A sixth object of the present invention is to be able to store energy insurrounding water in the form of kinetic energy.

At least one of the above objects is obtained according to claim 1.

Consequently, the invention relates to an aggregate for storing energyin the form of motion.

The said aggregate comprises a float body and conversion means, wherebythe said floating body is at least partially or completely placed in afluid and is arranged to rotate in direct contact with said fluid andthat said floating body together with said surrounding fluid is used bythe aggregate to store energy in the form of motion, and whereby energyis added to or extracted from the floating body and surrounding fluidthrough either said conversion means or via a part that absorbs energyof movements in a fluid and which the aggregate further could comprise,or that the energy is supplied or extracted from the float body and thesurrounding liquid by a combination of these.

By constructing an aggregate according to the invention, energy can bestored in the form of kinetic energy. The aggregate may comprise a partthat absorbs the energy and in this way e.g. a sea based wind-powerstation which can store energy can be constructed without the usage ofball bearings. In this case a floating body replaces the ball bearingsand handles the forces with the aid of the surrounding water, which isusually performed by bearings in power plants and flywheels. Byconstructing an aggregate according to the invention, the floating bodycan be used as an energy reservoir both for a short time and for a longtime. A possible wind-power station can then directly transfer itsenergy to the floating body in the form of motions. This energy isstored by rotation of the floating body and also a larger volume of thesurrounding water can be used to store energy in. When using for examplethe surrounding water to store energy, is it rotating along with thefloating body and in this way a large amount of mass is put into motion.The conversion means can for example consist of an electric generatorand be used to convert kinetic energy to electricity.

In one embodiment of the aggregate according to the invention, saidfloating body is interconnected to a part that absorbs the energywhereby said floating body sometimes is allowed to rotate even if saidpart rotates with a lower speed or has stalled relative to said floatingbody.

In one embodiment of the aggregate according to the invention, saidfloating body is interconnected to said part which comprises a verticalaxis power plant to absorb the energy in motions of a fluid.

In one embodiment of the aggregate according to the invention, saidfloating body is interconnected to said part which comprises ahorizontal power plant to absorb the energy in motions of a fluid.

In one embodiment of the aggregate according to the invention said fluidis comprised by a gas or a liquid.

In one embodiment of the aggregate according to the invention said partis comprised by an outer torus-shaped ring which surrounds the part thatabsorbs the energy and focus on the motion of the fluid through the partthat absorbs the energy.

In one embodiment of the aggregate according to the invention saidfloating body gives at least partially buoyancy to the aggregate in aliquid.

In one embodiment of the aggregate according to the invention, saidfloating body can increase its ability to store energy in form ofmotions by moving a mass from a more rotationally centralized cavityinto a less rotationally centralized cavity or by the float bodyincreasing its ability to store energy by increasing its mass and fillits cavities with for example surrounding liquid or a combination ofthose.

In one embodiment of the aggregate according to the invention, thefloating body is also arranged to use surrounding said liquid to storeenergy in the form of motion, whereby the float body is equipped withfins, blades or other types of surfaces to increase its contact tosurrounding liquid.

In one embodiment of the aggregate according to the invention, thefloating body is further arranged to use surrounding said liquid tostore energy in form of motions whereby structures or walls can beraised in the surrounding of aggregate to either restrict or control themotions of surrounding liquids that is used to store energy or to limitother flows, streams, motions or other possible effects.

In one embodiment of the aggregate according to the invention, the saidaggregate further comprises anchorage means adapted to connect saidaggregate with at least one anchor point.

In one embodiment of the aggregate according to the invention the saidanchorage means is meant to connect said aggregate with a base which atleast partially delimits said liquid.

In one embodiment of the aggregate according to the invention the saidanchorage means is meant to provide said aggregate with a non-rotatablepoint interconnected with said conversion means via a second part.

A second aspect of the invention relates the use of an aggregate tostore energy in form of motions or to extract energy from motions of afluid.

Problem Structure

The object of the present invention is mainly to provide an energystorage device which overcomes the problems associated with offshoreenergy storage devices according to the prior art.

Solution

The objects forming the basis of the present invention will be attainedif the bracket intimated by way of introduction is characterised in thatthe upper end of the central part is freely movable.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will be explained below by means of non-limitingexamples with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic, perspective view of an embodiment of theaggregate which stores energy in form of motions;

FIG. 2 shows a schematic, perspective view of another embodiment of theaggregate which stores energy in form of motions and absorbs motions ofthe air as a vertical axis power plant;

FIG. 3 shows a schematic, perspective view of a third embodiment of theaggregate which stores energy in form of motions and absorbs motions ofthe air as a vertical axis power plant;

FIG. 4 is a schematic, perspective view of the embodiment of theinvention according to FIG. 1, where a separating wall has been raisedaround the aggregate; and

FIG. 5 shows a schematic, perspective view of a fourth embodiment of theaggregate which stores energy in form of motions and absorbs motions ofwater as a vertical axis power plant;

FIG. 6 is a schematic, perspective view of yet another embodiment of theinvention showing an anchorage system with floating objects;

FIG. 7 shows a schematic, perspective view in detail of the lower partsof the float body in the embodiments according to FIGS. 1-6;

FIG. 8 shows a perspective view in cross-section of another embodimentof the lower parts of the aggregate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be described by means of examples of embodiments. Itshould nevertheless be understood that these embodiments only serve asto elucidate the present invention, the extent of protection of which islimited by the following claims.

FIG. 1 schematically shows the aggregate 10 intended to store energy inform of motions. The aggregate 10 comprises a floating body 14 and aconversion means 16. The floating body 14 is arranged to rotate indirect contact with the surrounding liquid 12, i.e. the sea water, andit is in this embodiment used for storing energy in form of rotation,whereby energy is supplied to floating body 14 by the conversion means16, which will convert mechanical energy into electric energy and viceversa. In this way large amounts of energy can be stored in form ofrotation. This can be especially suitable for a combination with seabased wind-power stations when the wind is strong. The energy can thenbe led as electricity to the conversion means 16 and be stored askinetic energy in form of rotation of the floating body 14.

Further, there is also an opportunity to use the surrounding water tostore kinetic energy generated by the motion of water masses. Also, byrotating the surrounding water around the floating body 14, even largeramounts of energy may be stored. In these cases whole electricity gridsmay be regulated from the aggregate 10, which will work as a largeenergy reservoir.

According to the invention, the aggregate 10 has an approximatelyvertical axis when it is in use. During use, and depending on theweather conditions, the axis may be somewhat tilted, but theconstruction of the aggregate, as well as its function, will ensure thatthe aggregate returns to its upright position, with an approximatelyvertical axis. The rotation of the aggregate 10 around its longitudinalaxis will assist in keeping the aggregate upright. The float body 14,arranged at a distance from a lower, anchored end of the aggregate 10,will also make sure that the aggregate remains upright. The upper, freeend 29 of the aggregate 10 will allow a tilting of its axis, which willallow adaptations to variations in the currents in the surroundingwater. At the same time, there is no need for bearings at the upper orlower end of the aggregate 10 besides for the anchorage means 15.

In FIG. 1 an anchorage means 15 shown, adapted to connect said aggregate10 with at least one anchorage point 25. It may also be considered toconnect anchorage means 15 to a boat, rock or some other possibleattachment point that may occur at sea, in lakes or in flowing streams.

The anchorage means 15 could be used to direct the aggregate 10 or partsof this in a desired direction in relation to the direction of motion ofthe surrounding fluid with the aid of the motion of the fluid. Thiscould be done by, for example, moving the attachment point on theanchorage means 15 on the aggregate 10. For example, a motor or ahydraulic system could be used to move the attachment point, which couldbe designed in a variety of ways. As the upper end 29 is free, only thelower end of the aggregate will have to be moved.

In rough weather the aggregate 10 may be exposed to less stressfulforces by directing or changing the position of the aggregate 10. FIG. 1shows an example where the anchorage means 15 is connected to theaggregate 10 with a base 18 which at least partly restricts the liquid12. In this example the anchorage means 15 is intended to provide saidaggregate 10 with a non-rotatable point interconnected to conversionmeans 16 by means of a second part 17. In this case the conversion means16 could be a generator that uses the second part 17 as a non-rotatablepoint and converts the relative rotation between the float body 14 andthis second part 17 into electric energy. The second part 17 could bereplaced with other types of anchorage means or fins so that thesurrounding water 12 or the base 18 will slow down the rotation. Anotheroption is that the aggregate 10 and anchorage means 16 areinterconnected directly to a fundament at the base. The aggregate 10 isused primarily at seas, in lakes or in streaming waters but can also beused in a pool or reservoir, filled with some other liquid than water.

By letting a float body 14 rotate, the conservation of momentum and theinertia of the water will create a stable platform and also theopportunity to store large amounts of energy. This construction alsocreates a possibility to provide one or more energy absorbing part 13,such as a horizontal axis wind-power station as shown in the embodimentof FIG. 2. The part 13, i.e. the wind power station, or the conversionmeans 16 can supply or absorb energy from the float body 14 where energyis stored as kinetic energy. It should however be mentioned that thepart 13 could be constructed in numerous different ways and that thereare for example many different types of vertical wind turbines thatcould be used.

FIG. 2 shows a schematic view of the aggregate 10 to store energy inform of motions in a float body 14 where the float body 14 isinterconnected with a part 13. In FIG. 2 the part 13 comprises avertical axis wind-power station, which absorbs energy from a fluid andstores it in the rotating float body 14 as kinetic energy. Such a fluidcould be a gas 11 or a liquid 12. In this case the float body 14 atleast partially gives buoyancy to the aggregate 10 in the liquid 12. Asmentioned above, it may also be considered using the surrounding waterto store rotational energy. It can for example be done by fins on thesides of the float body 14, which makes the water rotate around thefloat body 14.

Another possibility is to build the float body 14 very large and it mayalso be considered loading certain areas in float body 14 with a liquid12, for example. By moving a liquid or some other mass into the floatbody 14, the mass that holds the stored kinetic energy is altered. Thealteration of the mass will, in turn, alter the rotational speed of theaggregate, when the energy remains constant. In this way, the rotationalspeed can be adjusted and perhaps be used for an easier start up of therotation, to store even more energy and to keep an approximatelyconstant rotational speed.

An example of where one or more cavities are used is seen in FIG. 2. Aliquid can be pumped between two cavities with different positions; amore rotationally centralised cavity 19 one the one hand, and a lessrotationally centralised cavity 20 on the other hand. It means that thefloat body 14 can store a larger amount of kinetic energy at the samerotational speed, when the liquid is pumped from the rotationallycentralised cavity to the less rotationally centralised cavity. By thesame token, the rotational speed is changed when the distribution of themass is changed and the energy remains constant.

It should also be noted that the movement of masses could be performedin many ways, for example by means of valves, pumps, motors, movingwires etc. The centrifugal force could be used to move a mass. Anotherway is to simply let it fall down and make use of the difference inpotential energy at a higher position and a lower position. In this waya mass could be moved between a more rotationally centralised cavity 19and a less rotationally centralised cavity 20.

An example of an application of the invention could be to use ahorizontal power plant which supplies the float body 14 with energy,which is stored as kinetic energy and the conversion means 16 can laterconvert this energy to electric energy when the need arises. The floatbody 14 is still rotating, although at a lower speed as the energy isconsumed, and conversion means 16 can thereby continue to convertkinetic energy to electricity even when the wind has decreased.

An example of the aggregate 10 according to the present invention isshown in FIG. 2. It should be noted that this embodiment only serves asan example and that the included components and dimensions of these areonly one of a number of possible combinations which all fall within theextent of protection of the accompanying claims.

The aggregate 10 in FIG. 2 is placed at sea and is arranged to produceand store electricity when the part 13 is included, by means ofabsorbing a flow of a fluid, in this case air, and to absorb this flow,i.e. the wind, through the part 13, a vertical axis wind-power station.

Further, the float body 14 in FIG. 3 is an embodiment which may increaseits ability to store energy in the form of motions by moving a mass froma more rotationally centralized cavity 19 into a less rotationallycentralized cavity 20, or by letting the float body 14 increase itsability to store energy by increasing its mass and filling its cavitieswith, for example, the surrounding liquid 12, or a combination of thesemeasures. The float body 14 is provided with several cavities 19, 20,which may both receive a liquid temporarily, in order to store energy.When the stored energy is to be retrieved, either or both of thecavities 19, 20 may be emptied. In this way, the amount of mass or theposition of the mass that forms the base for the energy storage changes,or both, whereby the same amount of energy as before can be stored butat a different speed.

Another option is that different amounts of energy can be stored at thesame rotational speed of the float body 14. This option may be used forkeeping a correct phase while converting the energy to electricitythrough conversion means 16, relative the phase of the energy systems towhich the aggregate 10 could be connected.

The float body 14 of FIG. 3 can also be arranged to use the surroundingliquid 12 in order to store energy in form of motions, whereby the floatbody 14 can be equipped with fins, blades or other types of surfaces toincrease its contact with the surrounding liquid 12. This means that thepotential for storing energy becomes very large. It could be comparedwith a local current in the liquid 12 which is created when the floatbody 14 is supplied with energy and starts to rotate together withsurrounding liquid 12. This local current conserves the energy in formof rotational motion, and when the need of energy arises, the float body14 will receive the energy and the conversion will take place forexample through a conversion means 16, which in this example comprises agenerator. Another possibility is that the conversion means 16 comprisesa pump or that the energy is directly converted to hydrogen or oxygen orto produce fresh water through reverse osmosis. FIG. 3 shows a schematicview of the aggregate 10 to store energy in form of motions in a floatbody 14, where said float body 14 is interconnected with part 13, whichin this embodiment is a wind power station.

The part 13 consists of a vertical wind rotor in the describedembodiments, which means that the weight of the wind rotor must becarried by the float body, and that the energy that is absorbed isdirectly conveyed to the float body 14. The float body has a totallength of 250 meters where 100 meters is above the sea water surface.This means that the power plant does not need optimization of its weightwhen it is constructed and built, to the same degree as for the previoustechniques. The vertical forces that can arise on variation of theairflow, for example, will quickly be absorbed by the float body 14,which is rotating in the sea water and which will effectively stabilizethe aggregate 10. It is partly stabilised because of the conservation ofthe angular momentum, which means that when a relatively heavy object isrotating, the object resists from changes of its orientation. It is alsostabilised by the inertia of the water, which means that the aggregate10 will keep on rotating in the same direction, so it will not consumeenergy by moving around in the water. The energy that is absorbed by thepart 13, the wind rotor, is directly conveyed to the float body 14 andis stored there as kinetic energy. The float body 14 is now using seawater, which is pumped in by water pumps, for example, and fills thecavities that is more rotationally decentralised in float body 14.

In this case the sea water fills up the torus shaped ring 28 with adiameter of 230 meters, comprised by the float body 14, and positioned30 meters above sea water surface. It means that the mass which is thebase for the kinetic energy storage increases or is moved to a positionfurther away from the central axis of rotation and that a larger amountof energy can be stored. The part 13 increases the energy which isstored in aggregate 10 and the float body 14 is rotating with high speedand has filled all its cavities and moved its mass, which in this caseconsists of sea water. When the torus ring 28 is completely full withseawater and the rotational frequency is 0.08, the aggregate 10 canstore about 5 MWh. It means that a large amount of energy is stored inthe float body 14 with the torus ring 28.

When the wind and the motions of the air ceases the part 13 will stopabsorbing energy and conveying it to the float body 14. The float body14 will, however, still rotate with high speed and keep storing energyin form of a rotating motion. In this example the wind turbine and wingsabsorbing the energy is positioned by wires that also hold the torusring 28. In this example these wings can be moved from a lessrotationally centralised and a more rotationally centralised position.This can be used to change the energy storage capacity but also tochange the energy absorption of the turbine. It can also be used toalter friction losses. In a case when the wind or water velocity hasdecreased, it could be better to position the blades in a morerotationally centralised position. The velocity and friction lossescould with this technique be lowered.

A need of energy at the electricity grid may arise and the conversionmeans 16, which in this example consist of a generator, will start togenerate electricity into the grid. The second part 17 extends throughthe float body 14 and is connected to the conversion means 16 by meansof a shaft. It is also connected with anchorage means 15 to the base 18.Hereby the conversion means 16 is provided with a non-rotatable point,which it uses when it needs to convert the rotation and the kineticenergy to electricity. Now the float body 14 has exhausted its kineticenergy, but in order to maintain the speed of rotation the float body 14will, in this case, use the possibility to pump or open valves so thatmass can be moved from a less rotationally centralised cavity to a morerotationally centralised cavity. In this way the float body 14 may bedrained of its energy but still keep the same rotational velocity. Whenenough energy has been removed from the float body 14, the rotation willslow down and eventually the aggregate 10 will stand still withoutrotating.

The wind may be zero locally where the aggregate 10 has been installed,while it blows in other places in the electricity grid, which isinterconnected with aggregate 10. These places may be provided withwind-power stations, and if the need of electricity on the grid is low,the conversion means 16 will convert electricity from these wind-powerstations in different places into kinetic energy and store the energy inthe float body 14. The float body 14 will start rotating faster becauseof the energy that is supplied from the grid, and it will start to fillup the cavities with sea water again. The stored energy can later bere-supplied into the grid, to be used again, when the need arises. Inone example, where the float body 14 is built very large or where alsothe surrounding water is used for energy storing in a large scale, theaggregate 10 can become a very large energy reservoir.

By pumping sea water between different locations in the aggregate, forexample, the aggregate 10 may rise or sink in relation to the liquid 12,which could be useful during the installation or in severe weather. Atextreme weather conditions, the aggregate 10 could be located below thesurface for example. In water with large waves, the aggregate 10 may beraised.

The aggregate 10 according to the present invention could also comprisevarious sensors, control systems and communication systems. These may beincorporated to determine wave height, wave speed and more. It is alsopossible that aggregate 10, in severe weather for example, could belowered, which means moved to a location where the aggregate isprotected when factors such as liquid velocities, gas velocities or waveheights exceed a predetermined value. Since wave loads are highest atthe water surface, is it possible to significantly reduce the pressureon the aggregate 10. It should also be mentioned that aggregate 10 couldbe equipped with ladders, work cabins, construction sites for ships, andhelicopters or other types of transportation vehicles. It is alsoconsidered to equip the aggregate 10 with surface lots, floats, weightsor other types of constructions which provide buoyancy. One can alsoimagine that aggregate 10 is equipped with special coatings or materialto reduce fouling, friction or other effects. It is also considered toattach anchorage means 15 in a fundament or a buoy.

In the example where the float body 14 is arranged to provide a largesurface area, by fins, blades etc., and create local, surroundingcurrents in a liquid, it can also be useful to control or restrict theexpansion or directions of these currents by means of a wall 21 thatextends for example from the bottom of the sea to the surface, as shownin FIG. 4. Another possibility is to use natural formations or naturalcurrents to enhance or defend different impacts. It may also beconsidered that the liquid is located in a container at land and thatthe aggregate 10 is located in this container.

In some embodiments it may be preferred to restrict the surroundingwater with screens or walls 21. The screens or walls 21 in FIG. 4 couldhave weights at the bottom so that they have contact with the base 18 atthe bottom and they may be given buoyancy in the upper edge with forexample a floating buoy, to keep the screen or wall 21 in an uprightposition. Hereby it could be prevented that possible ocean currentswould carry off rotational energy that is stored in the surroundingwaters. This would make it possible to store very large amounts ofenergy in a cost efficient way in something that can be compared tolocal currents.

The part 13 could be designed in many ways for example as a horizontalaxis power plant to absorb the energy from motions in a fluid, such asair. In one example, with a horizontal axis power plant which absorbsenergy in the motion of a fluid, it may be preferred if part 13 isprovided with a ring 26 that surrounds the area 27 that absorbs theenergy, such as shown in FIG. 5. It means, in this example, that a torusshaped ring is situated at the outer ends of the rotor.

In FIG. 5 the part 13 is comprised by a vertical axis water-powerstation, which in this embodiment absorbs energy from the liquid 12. Theenergy is stored in the float body 14 as kinetic energy in form ofrotation. The float body 14 is allowed to rotate from time to time, evenif said part 13 rotates with a lower speed or has completely stalled inrelation to said float body 14. In this embodiment, the float body 14 atleast partially gives buoyancy to the aggregate 10 in the liquid 12.

Floating objects 23 or other equipment is usable in anchorage means 15as shown in FIG. 6. In FIG. 6 an example is shown, where the anchoragemeans 15 also connects to the float body 14 at a higher point. Thiscould be a good way to get a higher attachment to the float body and toenhance the stability. At the same time it could be a good way to letthe floating objects 23 give even more room for the anchorage system andaggregate 10 to move due to variations around its position.

FIG. 7 shows a detail view of the float body 14, the conversion means16, the second part 17 and the anchorage means 15 connecting theaggregate 10 to the base 18.

FIG. 8 shows a cross section of the lower part of the aggregate 10 andan example of how the lower sections of the aggregate 10 could be built.The float body 14 contains a ballast weight 24 and a lift shaft 22 sothat maintenance can be performed on the conversion means 16, in thiscase on the generator, generator axis, control systems etc. The secondpart 17 is shown interconnected to the generator 16 via an axis. Theanchorage means 15 is showed connecting the aggregate 10 to the base 18via an anchorage point 25. It should also be mentioned that maintenanceon the aggregate 10 could be performed in a number of different ways.Examples of this could be by divers or by letting the aggregate 10 tiltand float on the water surface. Other ways are by bringing the aggregate10 up on land, by moving the conversion means 16 inside of the aggregate10 and upwards, or by moving the conversion means 16 into the water andup to the surface for maintance.

Alternative Embodiments

It should also be mentioned that in further different embodiments it maybe handy to equip the aggregate 10 and the part 13 according to theembodiments shown and described above with other types of power plants,such as other types of blades, more blades or an extra set of bladeswhich can work in a more stable way and therefore could be used to startthe rotation of part 13. It is also possible to start the rotation byrunning a generator in reverse, as an electrical motor, or by addingother equipment. Examples of this can be a number of conversion means16, which may work at different rotation speeds, or several conversionmeans which supply energy while extracting energy with anotherconversion means. It would make it possible to supply a relativelyirregular electricity through a conversion means, for example generatedfrom wave power, and extract a more regular electricity through anotherconversion means. In this way, the aggregate 10 and float body 14 withconversion means 16 could work as an energy and electrical converter.

It should be noted that the present invention is in no way limited tothe above mentioned embodiments, but can be varied freely within thescope of the following claims. For example, the aggregate 10 could beequipped with fins, floating pontoons, weights or similar means to, forexample, influence the movement qualities of the aggregate 10.Furthermore, the energy can be supplied to or transported from the floatbody 14 in a number of additional ways besides the ones shown in thedescription above, for example by pumping up water to a reservoir on ahigher location. The energy can also be used to achieve reverse osmosis,to purify water from for example salt and/or polluted water. It is alsoconsidered to use the energy to produce hydrogen from the liquid 12,e.g. the sea water, and this hydrogen could be kept under pressure inthe liquid 12 and be further transported by boats for example. It isalso possible to store hydrogen in the second part 17 or in the floatbody 14.

The transmission of power could also to take place in magnetic fields,in which instance the components of the invention would be completelyencapsulated. It is possible to imagine that the part 16 or a partthereof is included in the part 17, the part 13 and/or the float body14. In such a case the part that generates the electric field would beincluded in one part 13, 14,17 and the part that induces the magneticfield would be included in another part 13, 14, 17. These parts wouldstill be completely encapsulated.

The aggregate 10 can also include a number of parts 13, floating bodies14 and conversion means 16 which will be interconnected to the secondpart 17. It should also be mentioned that the float body 14 can beproduced from a stiff material but said float body 14 can also beproduced from a flexible or inflatable material. It can be possible tofill the float body 14 with different types of gases or liquids withvarious densities to modify the buoyancy of float body 14. For example,helium gas could be used.

It should also be mentioned that the part 13, which absorbs the energy,could be produced from a stiff material, like the materials used inwind-power stations according to the prior art. But the part 13 couldalso be manufactured from a thin material, such as canvas. It is alsopossible to stretch canvas on sails or sailcloth to focus the motionsthrough the part 13.

1-13. (canceled)
 14. Offshore energy storage device (10), storing energyas rotational kinetic energy, comprising conversion means (16), anelongate, upright central part (14), which is rotatable around itslongitudinal axis, floating means arranged to keep it upright andfloating, a fly wheel (28) arranged concentrically around the centralpart and anchorage means (15) below the fly wheel (28) for anchoring tothe sea bed (18), characterized in that the upper end (29) of thecentral part (14) is freely movable.
 15. Offshore energy storage device(10) according to claim 14, characterized in that a lower section of thecentral part (14) has a substantially larger vertical extension than itshorizontal extension.
 16. Offshore energy storage device (10) accordingto claim 14, characterized in that the fly wheel (28) is arranged aroundan upper section of the central part (14), for keeping the fly wheel(28) above the water level (12) when the device (10) is floating inwater.
 17. Offshore energy storage device (10) according to claim 14,characterized in that the storage device (10) comprises a generatorcoupled to the central, rotating part (14) as well as to the anchoragemeans (15).
 18. Offshore energy storage device (10) according to claim17, characterized in that the generator is coupled to the central part(14) and the anchorage means (15) by a single axle.
 19. Offshore energystorage device (10) according to claim 14, characterized in that thestorage capacity of the storage device (10) is alterable by altering therotational speed either by supplying or removing energy via conversionmeans (16); energy absorbing part (13) or by changing the mass and/orthe position of the mass from the longitudinal axis.
 20. Offshore energystorage device (10) according to claim 14, characterized in that thestorage capacity of the storage device (10) is alterable by altering itsmass and/or its distance from the longitudinal axis.
 21. Offshore energystorage device (10) according to claim 14, characterized in that a firstpump is provided for introducing a liquid into and expelling a liquidfrom the storage device (10).
 22. Offshore energy storage device (10)according to claim 14, characterized in that a second pump is providedfor moving water between the fly wheel (28) and the central part (14).23. Offshore energy storage device (10) according to claim 14,characterized in that contact with the sea water, are provided on thelower section of the central part (14), for bringing the surrounding seawater to rotate with the storage device (10).
 24. Offshore energystorage device (10) according to claim 14, characterized in thatseparating walls (21) are arranged around the central part at a distancetherefrom, for separating a rotating liquid portion from the surroundingliquid.
 25. Offshore energy storage device (10) according to claim 14,characterized in that it comprises a wind turbine, for providing arotational force to the energy storage device (10).
 26. Offshore energystorage device (10) according to claim 14, characterized in that itcomprises a water turbine, for providing a rotational force to theenergy storage device (10).
 27. Offshore energy storage device (10)according to claim 15, characterized in that a lower section of thecentral part (14) has a substantially larger vertical extension than itshorizontal extension.